It is known that materials in sheets such as X-ray films or cards such as bank cards must have rounded corners.
According to a first known technique, such rounded corners are produced by making notches initially, having the shape of the rounded corner common to two adjacent sheets, on the edges of a moving strip and then cutting the strip in the middle of the said notch. The problem with such a technique lies in the difficulty in positioning the cutting device correctly with respect to the centre of the notch. In fact, the slightest error in the positioning of the cutting device will result in an incomplete rounded corner on one of the sheets and an unwanted strip at the end of the other sheet.
Another known technique involves stopping the process while positioning and producing the rounded corners on the sheet which has just been cut. This technique is of course detrimental from the point of view of productivity.
There are also other systems, such as line rotating systems, but which have great problems related to the complexity of the operations required for passing from one format to another.
FIG. 1, to which reference is now made, illustrates another known type of device enabling the corners of a pile of sheets to be rounded.
The device shown comprises principally an inclined plane 1 on which the sheets 2 are positioned, two reference surfaces 3, 4 at right angles to each other being provided on the said inclined plane 1 and against which the sheets are positioned under the effect of gravity. Advantageously vibration is applied to the reference surfaces so as to permit a better positioning of the sheets against the two reference surfaces 3, 4. The reference surfaces are separated from the bottom corner of the inclined plane 1 so as to be able to dispose a cutting tool between the said two reference surface 3, 4, the said cutting tool being designed so as to produce the desired shape of the rounded corner. In the example shown, the cutting device 5 comprises a curved blade movable in a reciprocating motion in the direction shown diagrammatically by the two directional arrows 6. The rounded corners in each corner of the pile are produced successively by moving the said pile manually.
The main problem with such a device lies in the positioning of the sheets against the reference surfaces. The device shown in FIG. 1 functions satisfactorily when the sheets in the pile are, initially, relatively well aligned so that the length of each sheet protruding beyond the edge of the normal alignment of the pile is sufficiently small to withstand a force applied axially without causing any deformation of the sheets with respect to the surface of the inclined plane 1.